Installing fA filter with Hab amp... problem / query


Afternoon all,

Ok - so installed the fa filter some weeks ago, been running fine.
Today, for example, (1325 on Sat), im gettng 85 birds out to 280 SM.

Unfortunately, I have both the filter and my new V3 from RTL SDR on the receiver side of the amp, not ideal - especially as I want to enable bias t on the V3 to power the hab.

So, currently rig is…

Ant / coax > F SMA > Hab M sma > Hab > Hab SMA > F/F SMA coupler > fA Filter M > SMA F > V3 M.

This works, and gives c85 birds, as above.

Now, if I change this to…

Ant / coax > F/SMA > fa Filter M > fA filter F > Hab M > hab M > f/f coupler > V3

Birds drops down to about 15, at really close range?

What am I doing wrong, and whats the solution?

Almost looks like the fA filters functionally directional?


Ant / coax > F/SMA > fa Filter M > fA filter F > Hab M > hab M > f/f coupler > V3

Why would you use 2 F/SMA and FA filter?
That reduces signal by insertion loss and degrades the SNR of the amp. And doesn’t add significant filtering.
Raise the gain for now, see what happens. But I won’t use that many filters.


sorry mate - probably me being overly detailed - that the f and m end of the same filter…



The first pic is how it should be, but doesnt work as expected, the 2nd pic is how I’ve got / had it that actually works…


Well, you have separate USB power to the amp, so you don’t need the T-power.
Secondly, probably the direct output of the amp is too high and overloads the receiver’s input. Adding the FA filter there adds some insertion loss and probably the signal drops just enough to get more clean signals.
That’s why I suggested to play with the gain level (of the tuner/receiver). Do you have it on AGC?


No, it o 38 or so at the moment - I was gonna do a full sweep using gain py, but wanted to get the filter before the amp so a) only amp’ing filtered signal and b) to enable the bias t so I can remove the micro usb power, in the hope of reducing any possible rf interference (not sure on the RF, just started looking into that).


So, as i believe its clearly better to have the filter before the amp (amping filtered signal only), and that the loss in birds could be due to overwhelming the V3 without the insertion loss - I’ll put it back so that the filter is indeed before the amp, then use gain py to reset the gain… ?


Doesn’t the amp have a filter of it’s own? I’d just put the amp near the antenna and enable the bias-t and be done with it.

Unless you overload the amp extra signal on the amp is not really a problem.

Have you tried without the FA filter?


Is there a gain adjustment at HAB amp itself? Software controlled or by hardware on HAB?


Hi guys (abcd :slight_smile: )

As the Hab is filtered anyway, have removed the fA filter.

Running the came up with positions= 0 planes= 2 at all gain settings…

Looking at the live map shows c80 birds still…

(I did edit the file to add all recognised gain settings, in case the amp needed a lower setting).


Open up the Hab amp to check if it is the right way around.
We have occasionally seen the modules inserted backwards, or the cases on backwards, depending on your point of view.
Yours looks to be correct though. The Dongle side has the USB power connector.
If it works without the amp then something that was added isn’t working. Check the connectors and the AMP itself.



Interesting - havent opened the Hab, but I’d have thought if the board had been inserted the wrong way, it would work very poorly, if at all?

My range / plots are usually pretty good (out to 300miles) - I’ve been using the Hab for a couple of years now.

Also, the live map shows c80 birds - just the script reports the above…

Is it still worth opening the hab to check that?


how many is c80?

No for some reason the script isn’t working no need to check the amp.

Just change gain manually. Try 20 30 and 40 as a start that should give you a good starting point.


Currently showing 79…


Either one of the connectors doesn’t seat perfectly with the other ones… or you need to adjust the gain.
You should see much more birds there, above London.


the script just isn’t working because he probably used the wrong one or butchered the copy paste.

no need for the script anyway.


Have set gain in mutability manually to 33.8, based on “generally best” from other threads.

Had that script working before, so gain was set based on results - but didnt record what it was, and the script reset it…


Try with 30 to start


Lol “butchered” - how rude! :wink:

Basically, just replaced the gains here…

measure_duration = 10 #secondsForEachGainSettingPerTest

ntests = 20 #numberOfCompleteCyclesAllGainSettings
gains = “20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 44.5 48.0 49.6”.split()
#gains = “36.4 38.6 40.2 42.1 44.5 48.0 49.6”.split()
#gains = “22.9 25.4 28.0 29.7 32.8 33.8 36.4”.split()

with the full range, in case my hab amp needed low than 20.7…

Have reverted to original range (As above) - this script did used to work…

I’ll try rebuilding that script again, in case I missed something, pretty sure I didnt tho.